$A$ long solenoid carrying a current produces a magnetic field $B$ along its axis. If the current is tripled and the number of turns per cm is halved, then the new value of the magnetic field will be:

$A$ long thin hollow metallic cylinder of radius $R$ carries a current $i$ ampere. The magnetic induction $B$ at a distance $r$ from the axis varies as shown in:

An imaginary north pole of $10 \, Am$ is rotating around an infinitely long current-carrying wire at $30 \, \text{revolutions/min}$ on a circular path. If the current in the wire is $5 \, A$, then calculate the work done in one second.

$A$ long cylindrical wire of radius $R$ carries a uniform current $I$ flowing through it. The variation of magnetic field $B$ with distance $r$ from the axis of the wire is shown by:

What is a solenoid? Provide information about the magnetic field through a qualitative discussion.

$A$ coaxial cable having radii $a, b$ and $c$ carries equal and opposite currents of magnitude $i$ in the inner and outer conductors. What is the magnitude of the magnetic induction at point $P$ outside of the cable at a distance $r$ from the axis?